Fuel injection control device

Abstract

To provide an engine control device for suppressing a decline in the fuel consumption rate while improving engine stall resistance at restarting fuel injection in the state of fuel cut and suppressing a torque fluctuation.SOLUTION: An engine control device 100 includes a fuel injection control part for controlling a fuel injection device to inject fuel into combustion chambers 31 of a plurality of cylinders, while executing fuel cut control when fuel cut conditions are satisfied, or allowing fuel injection in all cylinders through the state of cylinder-reduced fuel injection in which fuel injection is restarted only in part of the cylinders when the fuel cut conditions are not satisfied, and an amount increasing and correcting part for increasing and correcting the amount of fuel injection at the time of initial fuel injection after executing fuel cut, according to the amount of reverse flow air from an exhaust flow path. The number of the cylinders into which fuel is injected in the state of cylinder-reduced fuel injection is set to be greater in proportion as a torque fluctuation allowable amount set according to the travelling state of a vehicle is increased.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a fuel injection control device for controlling fuel injection of an engine.

Background Art

[0002] For example, in an engine for an automobile or the like, when a predetermined fuel cut condition is satisfied, fuel injection and ignition are stopped and the vehicle is coasted, and fuel cut is performed. Also, when a predetermined fuel cut return condition is satisfied during the execution of fuel cut, fuel injection and ignition are restarted. In an engine that performs fuel cut, it is desired to suppress a shock caused by a rapid increase in output torque at the time of fuel cut return (when fuel injection is restarted).

[0003] As a conventional technique related to control at the time of return from fuel cut, for example, in Patent Document 1, at the time of return from stratified combustion fuel cut, in order to reduce the shock due to torque step, when the required fuel injection amount required based on the torque correction amount is smaller than the minimum amount of fuel that can be injected by the fuel injection valve, the number of operating cylinders is calculated based on the difference between the minimum amount and the required fuel injection amount, and cylinder reduction operation is executed. Patent Document 2 describes that when interrupting fuel cut control and forcibly driving a fuel injection valve, only the fuel injection valve of a predetermined cylinder among all the cylinders of the engine is forcibly driven, and the ignition timing at that time is set on the retard side from the normal ignition timing, thereby suppressing the generated torque of the engine and ensuring a desired deceleration performance. Also, when interrupting fuel cut control and forcibly driving a fuel injection valve, it is described that a stable combustion state is maintained by controlling the fuel injection amount so that the air-fuel ratio is near the stoichiometric air-fuel ratio.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the fuel cut is executed and air flows backward from the exhaust passage into the cylinder, even if the fuel injection amount is set based on the intake air amount detected by the air flow meter when the fuel injection is resumed, due to the influence of the air remaining in the cylinder, the actual air-fuel ratio tends to be lean, the actual torque of the engine decreases with respect to the target torque, and the drivability (ease of driving) of the vehicle is impaired. Furthermore, when a disturbance such as an increase in load occurs during such torque down, there is also a concern that engine stall may occur. On the other hand, as described in Patent Document 2, if the in-cylinder air-fuel ratio at the time of fuel cut return is made near the stoichiometric air-fuel ratio, combustion stability can be ensured and engine stall resistance can be enhanced. However, in this case, if the ignition timing is set near MBT as in normal operation, the output torque of the engine becomes excessively high and the vehicle body shock due to torque fluctuation deteriorates. Here, in order to suppress the shock, if the ignition timing is retarded as in the technique described in Patent Document 2, the thermal efficiency of the engine decreases and the fuel consumption rate deteriorates. In view of the above problems, an object of the present invention is to provide an engine control device that improves engine stall resistance and suppresses torque fluctuation when fuel injection is resumed from the fuel cut state, and suppresses deterioration of the fuel consumption rate.

Means for Solving the Problems

[0006] To solve the above problems, an engine control device according to an aspect of the present invention is an engine control device that controls an engine having a plurality of cylinders, controls a fuel injection device that injects fuel into at least one of a combustion chamber and an intake port of the plurality of cylinders, executes fuel cut control to stop fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied, and when a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is resumed in some of the cylinders where fuel cut has been executed and fuel cut is continued in other cylinders, causes fuel injection to be performed in all cylinders; and an increment correction unit that corrects the fuel injection amount at the first fuel injection in the cylinders where fuel injection is resumed after the execution of the fuel cut to increase the amount with respect to the fuel injection at the second and subsequent times according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut. The fuel injection control unit after the predetermined fuel cut return condition is satisfied and until combustion injection is performed in all cylinders the reduced-cylinder fuel injection state during the period when it is is characterized in that the number of cylinders in which fuel injection is performed is set to increase as the allowable torque fluctuation amount set according to the running state of the vehicle increases. According to this, by correcting the fuel injection amount at the first fuel injection in the cylinders where fuel injection is resumed after the execution of the fuel cut to increase the amount according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut, it is possible to prevent the air-fuel ratio in the combustion chamber from becoming lean (as an example, near stoichiometry), stabilize the combustion state, prevent lean misfire, and improve the engine stall resistance. Further, by stabilizing the combustion state, it becomes easy to estimate the output torque of the engine. In addition, by performing reduced-cylinder fuel injection control in which fuel injection is performed only in some cylinders and fuel cut is continued in other cylinders, it is possible to suppress the output torque of the engine at the time of fuel cut return and suppress the vehicle body shock due to torque fluctuation. For this reason, it is not necessary to delay (retard) the ignition timing to suppress the output torque as in the prior art, and it is possible to prevent the fuel consumption rate from deteriorating due to the decrease in thermal efficiency caused by ignition retard. Furthermore, by setting the number of cylinders for fuel injection during the reduced-cylinder fuel injection control according to the allowable torque fluctuation set according to the driving state of the vehicle, it is possible to prevent the output torque of the engine from being excessively suppressed and the drivability (ease of driving) from being impaired, or conversely, to prevent the occurrence of vehicle body shock due to excessive torque fluctuation and improve the quality feeling of the vehicle.

[0007] Also, an engine control device according to another aspect of the present invention is an engine control device that controls an engine having a plurality of cylinders, controls a fuel injection device that injects fuel into at least one of the combustion chambers and intake ports of the plurality of cylinders, and executes fuel cut control to stop fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied. When a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is restarted in cylinders of some ranks in the ignition order of the cylinders in which fuel cut has been executed and fuel cut is continued in cylinders of other ranks, a fuel injection control unit that causes fuel injection to be performed in all cylinders, and an increment correction unit that corrects the fuel injection amount at the first fuel injection in the cylinders where fuel injection is restarted after the execution of the fuel cut to be increased with respect to the fuel injection at the second and subsequent times according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut. The fuel injection control unit after the predetermined fuel cut return condition is satisfied and until combustion injection is performed in all cylinders the reduced-cylinder fuel injection state during the period when it is is characterized in that the ratio of the number of cylinders in which fuel cut is continued to the number of cylinders in which fuel injection is performed is set to increase as the allowable torque fluctuation set according to the driving state of the vehicle increases. According to this, in addition to the same effect as the above invention, by setting the interval of fuel injection (combustion) during the reduced-cylinder fuel injection control to be longer as the allowable torque fluctuation decreases, the torque fluctuation at the time of fuel cut return can be made gentler. Also, an engine control device according to another aspect of the present invention is an engine control device that controls an engine having a plurality of cylinders, controls a fuel injection device that injects fuel into at least one of the combustion chambers and intake ports of the plurality of cylinders, and executes fuel cut control to stop fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied. When a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is restarted in cylinders of some ranks in the ignition order of the cylinders in which fuel cut has been executed and fuel cut is continued in cylinders of other ranks, a fuel injection control unit that causes fuel injection to be performed in all cylinders, and an increment correction unit that corrects the fuel injection amount at the first fuel injection in the cylinders where fuel injection is restarted after the execution of the fuel cut to be increased with respect to the fuel injection at the second and subsequent times according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut. The fuel injection control unit sets the ratio of the number of cylinders in which fuel cut is continued to the number of cylinders in which fuel injection is performed in the reduced-cylinder fuel injection state to increase as the allowable torque fluctuation amount set according to the running state of the vehicle increases, Set the interval during which the fuel injection is performed in the reduced-cylinder fuel injection state to be longer as the allowable torque fluctuation decreases characterized in that. According to this, when performing fuel cut recovery in a state where the allowable torque fluctuation amount is low, the output torque fluctuation of the engine can be made gentler, and the vehicle body shock caused by torque fluctuation can be more effectively suppressed.

[0008] In each of the above inventions, the fuel injection control unit can be configured to set the allowable torque fluctuation amount to increase in accordance with an increase in the deceleration of the vehicle during the execution of the fuel cut. According to this, during gentle coasting (coasting) with a relatively low deceleration, since the vehicle occupants are likely to feel the vehicle body shock caused by torque fluctuation, by setting the allowable torque fluctuation amount low, the effect of suppressing the vehicle body shock can be enhanced. On the other hand, in a state where the deceleration is relatively high, for example, when accompanied by a braking operation, there is a high possibility of immediately shifting to re-acceleration after the deceleration ends when entering a curve (corner) or an intersection, etc. In such a case, by setting the allowable torque fluctuation amount large, the rise of the output torque of the engine can be accelerated, and the drivability (ease of driving) of the vehicle can be enhanced.

[0009] In each of the above inventions, the engine has an intake air amount control unit that controls the intake air amount of each of the plurality of cylinders separately, and the engine control device is configured to include a torque control unit that adjusts the output torque of the engine in the cylinder reduction fuel injection state by adjusting the intake air amount of the cylinders that continue the fuel cut. According to this, it becomes possible to control the output torque of the engine at the time of fuel cut recovery not only by the number of cylinders to be reduced in the cylinder reduction fuel injection control but also by the pump loss of the cylinders that continue the fuel cut, enabling precise torque control.

Effect of the Invention

[0010] As described above, according to the present invention, it is possible to provide an engine control device that improves the engine stall resistance and suppresses torque fluctuation when restarting fuel injection from the fuel cut state, and suppresses the deterioration of the fuel consumption rate.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0012] <First Embodiment> Hereinafter, a first embodiment of a fuel injection control device to which the present invention is applied will be described. The fuel injection control device of the first embodiment is provided, for example, in a horizontally opposed four-cylinder gasoline direct injection engine mounted as a driving power source in an automobile such as a passenger car.

[0013] FIG. 1 is a diagram schematically showing the configuration of an engine having the fuel injection control device of the first embodiment. The engine 1 includes a crankshaft 10, a cylinder block 20 (20R, 20L), cylinder heads 30 (30R, 30L), an intake system 40, an exhaust system 50, an EGR device 60, an engine control unit 100, and the like.

[0014] The crankshaft 10 is a rotating shaft that serves as the output shaft of the engine 1. A power transmission mechanism such as a transmission (not shown) is connected to one end of the crankshaft 10. The crankshaft 10 is formed with a crankpin disposed eccentrically from the rotation axis. A piston P (see FIG. 3) is connected to the crankpin via a connecting rod (not shown). At the end of the crankshaft 10, a crank angle sensor 11 for detecting the angular position of the crankshaft is provided. The output of the crank angle sensor 11 is transmitted to the engine control unit 100. Based on the output of the crank angle sensor 11, the engine control unit 100 calculates the engine speed (crankshaft rotation speed).

[0015] The cylinder block 20 is configured as a two-piece structure consisting of a right cylinder block 20R and a left cylinder block 20L so as to sandwich the crankshaft 10 from the left and right directions when the crankshaft 10 is mounted vertically in the vehicle body. A crankcase portion is provided at the central portion of the cylinder block 20. The crankcase portion is a space portion for accommodating the crankshaft 10. In the crankcase portion, a main bearing for rotatably supporting the journal portion of the crankshaft 10 is provided. Inside the right cylinder block 20R and the left cylinder block 20L arranged on the left and right sides sandwiching the crankcase portion, cylinders C (see FIG. 3) into which the piston P is inserted and reciprocates are formed, for example, two cylinders at a time (in the case of a four-cylinder engine).

[0016] A water temperature sensor 21 is provided in the cylinder block 20. The water temperature sensor 21 is a temperature sensor for detecting the temperature of the cooling water of the engine 1. The output of the water temperature sensor 21 is transmitted to the engine control unit 100.

[0017] The cylinder heads 30 (right cylinder head 30R, left cylinder head 30L) are respectively provided at the ends (left and right ends) of the cylinder block 20 on the side opposite to the crankshaft 10. The cylinder head 30 is configured to include a combustion chamber 31, a spark plug 32, an intake port 33, an exhaust port 34, an intake valve 35, an exhaust valve 36, an intake camshaft 37, an exhaust camshaft 38, an injector 39, etc. The combustion chamber 31 is formed by, for example, recessing a portion of the cylinder head 30 facing the piston crown surface in a pent-roof shape. The spark plug 32 generates a spark in response to an ignition signal from the engine control unit 100 and ignites the air-fuel mixture. The spark plug 32 is provided at the center of the combustion chamber 31 as viewed from the axial direction of the cylinder.

[0018] The intake port 33 is a flow path for introducing combustion air (fresh air) into the combustion chamber 31. The exhaust port 34 is a flow path for discharging the burned gas (exhaust gas) from the combustion chamber 31. The intake valve 35 and the exhaust valve 36 open and close the intake port 33 and the exhaust port 34 at a predetermined valve timing. For example, two intake valves 35 and two exhaust valves 36 are provided for each cylinder. The intake valve 35 and the exhaust valve 36 are opened and closed by the intake camshaft 37 and the exhaust camshaft 38 that rotate synchronously at half the rotational speed of the crankshaft 10. The intake valve 35 is provided with a variable valve lift mechanism (not shown) capable of continuously or stepwise changing the valve lift for each cylinder. The variable valve lift mechanism has a function of controlling the pump loss of the cylinders that continue fuel cut in the later-described cylinder reduction fuel injection control, and functions as an intake air amount control unit of the present invention. The cam sprocket portions of the intake camshaft 37 and the exhaust camshaft 38 are provided with a valve timing variable mechanism (not shown) that advances or retards the phase of each camshaft to change the valve opening timing and the valve closing timing of each valve. The injector 39 injects fuel into the combustion chamber 31 in response to an opening signal issued by the engine control unit 100 to form an air-fuel mixture. The injector 39 is provided such that the nozzle portion for injecting fuel is exposed into the cylinder from the region on the intake port 33 side of the inner surface of the combustion chamber 31.

[0019] The intake system 40 is an intake device that introduces air and guides it into the intake port 33. The intake system 40 includes an intake duct 41, a chamber 42, an air cleaner 43, an air flow meter 44, a throttle valve 45, an intake manifold 46, an intake pressure sensor 47, etc.

[0020] The intake duct 41 is a flow path that introduces outside air and guides it into the intake port 33. The chamber 42 is a space portion provided in communication with the vicinity of the inlet portion of the intake duct 41. The air cleaner 43 filters air and removes dust and the like. The air cleaner 43 is provided on the downstream side of the communication portion with the chamber 42 in the intake duct 41. The air flow meter 44 measures the air flow rate (intake air amount of the engine 1) passing through the intake duct 41. The air flow meter 44 is provided near the outlet of the air cleaner 43. The output of the air flow meter 44 is transmitted to the engine control unit 100.

[0021] The throttle valve 45 is a butterfly valve that adjusts the air flow rate and controls the output of the engine 1. The throttle valve 45 is provided near the connection portion with the intake manifold 46 in the intake duct 41. The throttle valve 45 is driven to open and close by an electric throttle actuator (not shown) according to the target throttle opening degree set by the engine control unit 100 in response to the driver required torque and the like. In addition, the throttle valve 45 is provided with a throttle sensor that detects its opening degree, and its output is transmitted to the engine control unit 100. The intake manifold 46 is a manifold that distributes air to the intake ports 33 of each cylinder. The intake manifold 46 is provided on the downstream side of the throttle valve 45. The intake pressure sensor 47 detects the pressure of the air (intake pressure) in the intake manifold 46. The output of the intake pressure sensor 47 is transmitted to the engine control unit 100.

[0022] The exhaust system 50 is an exhaust device that discharges the exhaust gas discharged from the exhaust port 34 to the outside. The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe 52, a front catalyst 53, a rear catalyst 54, a silencer 55, an air-fuel ratio sensor 56, a rear O2 sensor 57, etc.

[0023] The exhaust manifold 51 is a manifold that collects the exhaust gas discharged from the exhaust ports 34 of each cylinder. The exhaust pipe 52 is a pipe that discharges the exhaust gas discharged from the exhaust manifold 51 to the outside. The front catalyst 53 and the rear catalyst 54 are provided in the middle part of the exhaust pipe 52, and each is provided with a three-way catalyst for purifying HC, NO X , CO, etc. The front catalyst 53 is provided adjacent to the outlet of the exhaust manifold 51, and the rear catalyst 54 is provided on the outlet side of the front catalyst. The silencer 55 reduces the acoustic energy of the exhaust gas. The silencer 55 is provided near the outlet of the exhaust pipe 52.

[0024] The air-fuel ratio sensor 56 is provided between the outlet of the exhaust manifold 51 and the inlet of the front catalyst 53. The rear O2 sensor 57 is provided between the outlet of the front catalyst 53 and the inlet of the rear catalyst 54. The air-fuel ratio sensor 56 and the rear O2 sensor 57 both detect the amount of oxygen in the exhaust gas by generating an output voltage corresponding to the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 56 is a linear output sensor capable of detecting the oxygen concentration in a wider range of air-fuel ratios than the rear O2 sensor 57. The outputs of the air-fuel ratio sensor 56 and the rear O2 sensor 57 are both transmitted to the engine control unit 100.

[0025] The EGR device 60 performs exhaust gas recirculation (EGR) that extracts a part of the exhaust gas from the exhaust manifold 51 as EGR gas and introduces it into the intake manifold 46. The EGR device 60 includes an EGR passage 61, an EGR cooler 62, an EGR valve 63, etc.

[0026] The EGR passage 61 is a pipeline that introduces exhaust gas (EGR gas) from the exhaust manifold 51 into the intake manifold 46. The EGR cooler 62 cools the EGR gas flowing through the EGR passage 61 by heat exchange with the cooling water of the engine 1. The EGR cooler 62 is provided in the middle of the EGR passage 61. The EGR valve 63 is a metering valve that adjusts the flow rate of the EGR gas passing through the EGR passage 61. The EGR valve 63 is provided on the downstream side of the EGR cooler 62 in the EGR passage 61. The EGR valve 63 has a valve body that is driven by an electric actuator such as a solenoid to open and close, and its opening degree is controlled by the engine control unit 100 using an opening degree map set based on a predetermined target EGR rate (EGR gas flow rate / intake air flow rate).

[0027] The engine control unit 100 comprehensively controls the engine 1 and its auxiliary equipment. The engine control unit 100 includes information processing means such as a CPU, storage means such as a RAM and a ROM, an input / output interface, and a bus for connecting these components. In addition, the engine control unit 100 is provided with an accelerator pedal sensor 101 that detects the amount of depression of an accelerator pedal (not shown) by the driver.

[0028] The engine control unit 100 is also connected to an atmospheric pressure sensor 110 and an acceleration sensor 120. The atmospheric pressure sensor 110 is a pressure sensor that detects the air pressure (atmospheric pressure) in the atmosphere around the vehicle. The acceleration sensor 120 detects the acceleration acting in the longitudinal direction of the vehicle body. During coasting of the vehicle in a fuel cut state, the acceleration sensor 120 detects the deceleration of the vehicle. The output of the acceleration sensor 120 is used, for example, to set the number of cylinders for cylinder cut in the cylinder cut fuel injection control described later.

[0029] The engine control unit 100 has a function of setting a driver demand torque based on the output of the accelerator pedal sensor 101 and the like. The engine control unit 100 controls the throttle valve opening, supercharging pressure, fuel injection amount, fuel injection timing, ignition timing, valve timing, etc., so that the torque actually generated by the engine 1 approaches the set driver demand torque. The engine control unit 100 has an injection control unit 102 that sets the fuel injection amount and drives an injector to perform fuel injection. During normal operation, the injection control unit 102 sets a basic fuel injection amount based on the intake air amount detected by the air flow meter 44, and performs air-fuel ratio feedback control to correct the actual air-fuel ratio so that it falls within the active range of the three-way catalyst based on the output of the air-fuel ratio sensor 56.

[0030] In addition, when a predetermined fuel cut condition is satisfied, the engine control unit 100 executes a fuel cut that stops fuel injection and ignition. As fuel cut conditions, for example, the vehicle's traveling speed (vehicle speed) being equal to or higher than a predetermined value, the engine speed being equal to or higher than a predetermined value, the driver required torque being equal to or lower than a predetermined value (for example, being zero), etc. can be cited. After performing fuel cut, when a predetermined fuel cut return condition is satisfied (typically when the above fuel cut conditions are no longer satisfied), the engine control unit 100 ends the fuel cut (returns from fuel cut) and resumes fuel injection and ignition.

[0031] When starting fuel cut from the fuel injection state, in order to avoid a sudden change in the output torque of the engine, the engine control unit 100 performs control to sequentially start fuel cut for each cylinder at time intervals. For example, in a horizontally opposed four-cylinder engine like the first embodiment, the ignition order is in the order of the first cylinder, the third cylinder, the second cylinder, and the fourth cylinder. When starting fuel cut, the engine control unit 100 sequentially stops the fuel injection and ignition of each cylinder, for example, in the same order as the ignition order.

[0032] When the engine control unit 100 executes fuel cut and the vehicle travels by inertia, in order to obtain a desired deceleration feeling and deceleration due to the pumping loss of engine 1, the opening degree control of the throttle valve 45 is performed. For example, when the deceleration of the vehicle is greater than a predetermined target deceleration, the opening degree of the throttle valve 45 is increased to suppress the pumping loss, and when it is smaller than the target deceleration, control is performed to decrease the opening degree of the throttle valve 45 to increase the pumping loss.

[0033] Also, when returning from fuel cut, the engine control unit 100 performs the fuel increment correction described below in order to prevent the air-fuel ratio from becoming lean due to the reverse flow of air from the exhaust system 50 into the cylinder C. The engine control unit 100 includes an injection amount correction unit 103 that corrects the fuel injection amount to increase it according to the amount of reverse flow air from the exhaust side into the combustion chamber 31 during fuel cut.

[0034] Figure 2 is a diagram showing the mechanism of reverse flow from the exhaust passage into the cylinder during fuel cut of the engine according to the first embodiment. Figures 2(a), 2(b), and 2(c) show schematic cross-sections taken by cutting the cylinder with a plane including the central axis. Figure 2(a) shows a state where the piston P is near the bottom dead center at the end of the combustion stroke and the exhaust valve 36 is open (point A in FIG. 3). Figure 2(b) shows a state where the piston P is moving toward the top dead center during the middle of the exhaust stroke (point B in FIG. 3). Figure 2(c) shows a state where the piston P is near the top dead center at the end of the exhaust stroke and the exhaust valve 36 is closed (point C in FIG. 2).

[0035] As shown in Figure 2(a), when the piston P is near the bottom dead center after the combustion stroke and the exhaust valve 36 opens, air flows reversely and enters from the exhaust port 34 and the exhaust system 50 side into the cylinder C. After that, as shown in Figure 2(b), when the piston P moves toward the top dead center, the residual exhaust gas in the cylinder C and the air that has flowed reversely from the exhaust system 50 etc. are pushed out from the exhaust port 34 to the exhaust system 50 side. As shown in Figure 2(c), when the piston P is near the top dead center, the exhaust valve 36 is closed. At this time, the gas remaining in the cylinder C is in a state where the residual exhaust gas and the air (fresh air) that has flowed reversely from the exhaust system 50 are mixed, and the amount of air contained here cannot be detected by the air flow meter 44.

[0036] Figure 3 is a diagram showing an example of the pressure change in the cylinder during fuel cut in the engine according to the first embodiment. In Figure 3, the horizontal axis represents the crank angle, and when the rotational speed of the crankshaft 10 is constant, it can also be read as time. The vertical axis represents the pressure in the cylinder C. During fuel cut when combustion does not occur in the combustion chamber 31 and there is no heat supply by combustion, in the compression stroke, it can be regarded as approximately adiabatic compression, and in the expansion stroke, it can be regarded as approximately adiabatic expansion. Therefore, the in-cylinder pressure at the end of the expansion stroke becomes equal to the in-cylinder pressure at the start of the compression stroke. At this time, the intake pipe pressure (the pressure in the intake manifold 46) becomes lower than the atmospheric pressure due to the throttling effect of the throttle valve 45. Also, the in-cylinder pressure from the intake stroke to the start of the compression stroke becomes even lower than the intake pipe pressure due to the flow path resistance such as the intake port 33.

[0037] On the other hand, the pressure in the exhaust manifold 51 becomes approximately equal to the atmospheric pressure because the rear end of the exhaust manifold 51 is open to the atmosphere. During fuel cut, the in-cylinder pressure when the exhaust valve 36 opens becomes equal to the in-cylinder pressure when the intake stroke ends and the intake valve 35 closes. Therefore, when the exhaust valve 36 opens, a reverse flow occurs from the exhaust port 34 side into the cylinder C. Also, in the exhaust stroke, the gas pushed out from the cylinder C to the exhaust port 34 side is mainly air and contains a part of the residual exhaust gas during fuel cut. When the crankshaft 10 of the engine 1 rotates during fuel cut and the cycles accumulate, the amount of air staying in the exhaust system 50 increases, and the proportion of air in the gas flowing back into the cylinder C also increases, and scavenging progresses.

[0038] In FIG. 3, the pressure transition immediately after the start of fuel cut is shown by a solid line, and the pressure transition when time has elapsed after the start of fuel cut is shown by a broken line. Due to the influence of the air flowing back from the exhaust system 50 as described above, when fuel cut is executed, as shown in FIG. 3, the in-cylinder pressure rises. When fuel cut can be performed in a cylinder, the increase amount of the in-cylinder pressure increases according to the increase in the number of cylinders in which fuel cut is being performed.

[0039] Thus, when air flows backward from the exhaust side into the cylinder during fuel cut, if the fuel injection amount is set based on the output of the air flow meter 44 when fuel injection resumes at the end of fuel cut, the air-fuel ratio becomes lean (excess air), the output torque of the engine 1 decreases, and the drivability of the vehicle is impaired, or there is concern that misfire or engine stall may occur. Therefore, in the fuel injection control device of the first embodiment, when fuel injection resumes after fuel cut (when fuel cut resumes), the fuel injection amount increase correction described below is performed. Further, in the fuel injection control of the first embodiment, in order to suppress the torque shock at the time of fuel cut resumption, the cylinder reduction fuel injection control described below is performed. FIG. 4 is a flowchart showing the control at the end of fuel cut in the fuel injection control device of the first embodiment. Hereinafter, the process will be described step by step.

[0040] <Step S01: Fuel cut end determination> The engine control unit 100 determines whether or not the fuel cut state has become insufficient (fuel cut resume condition satisfied) from the state in which fuel cut is being executed and it is time to end the fuel cut. If it is time to end the fuel cut, the process proceeds to step S02, and in other cases, the series of processes ends.

[0041] <Step S02: Acquisition of various parameters> The engine control unit 100 acquires information regarding the rotational speed of the crankshaft 10, the opening degree of the throttle valve 45, the coolant temperature, the atmospheric pressure, and the deceleration based on the outputs of the respective sensors. Thereafter, the process proceeds to step S03.

[0042] <Step S03: Setting of the number of cylinders with cylinder reduction> The engine control unit 100 sets the number of cylinders to be reduced in fuel injection at the time of fuel cut return at the vehicle deceleration detected in step S02. FIG. 5 is a diagram showing the correlation among vehicle deceleration, torque fluctuation allowable amount, and the number of cylinders to be reduced in the engine control device according to the first embodiment. The number of cylinders to be reduced is set according to the allowable value of the shock generated on the vehicle body due to the output torque fluctuation of engine 1 at the time of fuel cut return. The torque fluctuation allowable amount is set to increase as the vehicle deceleration increases. The number of cylinders to be reduced is set to decrease (so that the number of cylinders to be fuel-injected increases) as the torque fluctuation allowable amount increases. Thereafter, the process proceeds to step S04.

[0043] <Step S04: Estimation of reverse flow air amount and setting of basic increment correction term> The engine control unit 100 estimates the amount of air flowing back from the exhaust side into cylinder C during fuel cut (reverse flow air amount), and sets a basic increment correction term set in consideration of stoichiometric combustion of the estimated reverse flow air amount. The reverse flow air amount can be obtained, for example, using a reverse flow air amount map from which the reverse flow air amount is read out based on the rotational speed of engine 1 (the rotational speed of crankshaft 10) and the opening degree of throttle valve 45. Also, it is preferable to set the reverse flow air amount map according to the number of cylinders performing fuel cut, respectively. The reverse flow air amount map can be set for each model of engine 1, for example, experimentally or using simulation. In the case of an engine having a variable valve timing mechanism, since the reverse flow air amount changes depending on the valve timing, a configuration may be provided with a plurality of reverse flow air amount maps corresponding to different valve timings. Thereafter, the process proceeds to step S05.

[0044] <Step S05: Atmospheric pressure correction> The engine control unit 100 corrects the basic increment correction term set in step S05 based on the output of the atmospheric pressure sensor 110. When the atmospheric pressure detected by the atmospheric pressure sensor 110 is lower than the standard pressure, the pressure in the exhaust system 50 also decreases, and the amount of backflow air into the cylinder C also decreases. Therefore, a decrease correction is performed on the basic increment correction term. The amount of decrease correction at this time is set to increase in response to the decrease in atmospheric pressure. Thereafter, the process proceeds to step S06.

[0045] <Step S06: Correction at low water temperature> The engine control unit 100 detects the coolant water temperature of the engine 1 based on the output of the water temperature sensor 21. In a low temperature state where the coolant water temperature is below a predetermined threshold value, an increment correction is performed on the basic increment correction term after correction in step S05. The amount of increment correction at this time may be increased in response to the decrease in the coolant water temperature. Thereafter, the process proceeds to step S07.

[0046] <Step S07: Determination of fuel injection amount after increment correction> The engine control unit 100 adds up the fuel amount corresponding to the basic increment correction term corrected in steps S05 and S06 and the fuel amount set based on the intake air amount detected by the air flow meter 44 to determine the final fuel injection amount. Thereafter, the process proceeds to step S08.

[0047] <Step S08: Judgment on whether there is a cylinder with reduced cylinders> The engine control unit 100 determines in step S03 whether the number of cylinders with reduced cylinders of one or more is set. If the number of cylinders with reduced cylinders of one or more is set, the process proceeds to step S10; otherwise, the process proceeds to step S09.

[0048] <Step S09: Restart of fuel injection for all cylinders> Based on the fuel injection amount determined in step S07, the engine control unit 100 resumes fuel injection control for each cylinder (all cylinders) of engine 1. At the time of the first fuel injection in each cylinder, the fuel injection amount after the above-described increment correction is used so that the air-fuel ratio in the combustion chamber is near the theoretical air-fuel ratio (stoichiometry). Also, in the second and subsequent fuel injections in each cylinder, the normal fuel injection control based on the output of the air flow meter 44 is resumed, and then the air-fuel ratio feedback control is resumed. Thereafter, a series of processes is terminated.

[0049] <Step S10: Execution of cylinder reduction fuel injection> The engine control unit 100 executes cylinder reduction fuel injection control to resume fuel injection to the remaining cylinders while continuing fuel cut with the number of cylinders for cylinder reduction set in step S03. As a result, engine 1 is in a cylinder reduction fuel injection state where fuel injection is performed only in some cylinders and fuel cut continues in other cylinders. At this time, in the fuel injection in the cylinders where fuel injection is performed, the fuel injection amount after the above-described increment correction is used so that the air-fuel ratio in the combustion chamber is near the theoretical air-fuel ratio. For example, in the case of engine 1 having an ignition order of the first cylinder - the third cylinder - the fourth cylinder - the second cylinder, when reducing one cylinder, for example, fuel cut can be continued in the second cylinder and fuel injection can be resumed in the other cylinders. Also, when reducing two cylinders, the fuel injection can be resumed in the first cylinder and the fourth cylinder so that the combustion intervals are equal, and fuel cut can be continued in the second cylinder and the third cylinder. Also, when reducing three cylinders, fuel injection can be performed only in the first cylinder and fuel cut can be continued in the other cylinders. Note that the above combination of the cylinders where fuel injection is performed and the cylinders where fuel cut continues is an example and can be changed as appropriate. Note that the ignition timing in the cylinders where fuel injection is performed is the same as that during normal operation of engine 1 (typically near MBT where the output torque is maximum).

[0050] Also, during the execution of the cylinder reduction fuel injection control, the engine control unit 100 performs the output torque control of the engine 1 by the cylinder reduction number of cylinders described above and the valve lift control of the cylinders in which fuel cut is being continued. For example, when the valve lift is suppressed in the cylinder during which fuel cut is being continued, the pump loss in the cylinder increases, and the output torque of the engine 1 can be suppressed. The engine control unit 100 and the valve lift variable mechanism of the intake valve 35 function as the torque control unit of the present invention. Thereafter, in the cylinder reduction fuel injection control, after performing fuel injection a predetermined number of times, the engine control unit 100 ends the cylinder reduction fuel injection control and resumes fuel injection for all cylinders. The engine control unit 100 ends the increment correction according to the reverse flow air amount, sets the fuel injection amount based on the output of the air flow meter 44, and returns to the air-fuel ratio feedback control that appropriately performs feedback correction based on the output of the air-fuel ratio sensor 56. Thereafter, a series of processes ends (returns).

[0051] According to the first embodiment described above, the following effects can be obtained. (1) By increasing the fuel injection amount at the first fuel injection of the cylinder where fuel injection is resumed after the execution of fuel cut according to the reverse flow air amount from the exhaust passage to the combustion chamber during the execution of fuel cut, it is possible to prevent the air-fuel ratio in the combustion chamber from becoming lean (as an example, near stoichiometry), stabilize the combustion state, prevent lean misfire, and improve the engine stall resistance. Also, by performing the cylinder reduction fuel injection control in which fuel injection is performed only in some cylinders and fuel cut is continued in other cylinders, the output torque of the engine at the time of fuel cut return can be suppressed, and the vehicle body shock due to torque fluctuation can be suppressed. Therefore, it is not necessary to delay (retard) the ignition timing to suppress the output torque as in the prior art, and it is possible to prevent the fuel consumption rate from deteriorating due to the decrease in thermal efficiency caused by ignition retard. Furthermore, by setting the number of cylinders for fuel injection during deceleration fuel injection control according to the allowable torque fluctuation set according to the driving state of the vehicle, it is possible to prevent the output torque of the engine from being excessively suppressed and the drivability (ease of driving) from being impaired, or conversely, to prevent the occurrence of vehicle body shock due to excessive torque fluctuation and improve the quality of the vehicle. (2) During gentle coasting with a relatively low deceleration (during coasting), since the vehicle occupants are likely to feel the vehicle body shock due to torque fluctuation, by setting the allowable torque fluctuation to a low value, the suppression effect of the vehicle body shock can be enhanced. On the other hand, in a state where the deceleration is relatively high, for example, when accompanied by a braking operation, there is a high possibility of immediately shifting to re-acceleration after the deceleration ends when entering a curve (corner) or an intersection, etc. In such a case, by setting the allowable torque fluctuation to a large value, the rise of the output torque of the engine can be accelerated, and the drivability (ease of driving) of the vehicle can be enhanced. (3) By controlling the valve lift of the cylinders that continue fuel cut during deceleration fuel control to control the output torque of engine 1, the output torque of engine 1 at the time of fuel cut return can be controlled not only by the number of cylinders decelerated in the deceleration fuel injection control but also by the pump loss of the cylinders that continue fuel cut, enabling precise torque control.

[0052] <Second Embodiment> Next, a second embodiment of the engine control device to which the present invention is applied will be described. In the second embodiment, the deceleration fuel injection control according to the allowable torque fluctuation is performed by injecting fuel in some of the ignition orders of each cylinder and continuing fuel cut (skipping fuel injection) in other orders. In the second embodiment, for example, similar to the first embodiment, the allowable torque fluctuation is set according to the deceleration of the vehicle, and as the allowable torque fluctuation decreases, the number of interval times of the ignition order in which fuel injection is performed is increased (the number of cylinders in which fuel cut is continued is increased).

[0053] In the second embodiment, after fuel injection is performed in a certain cylinder, fuel cut is performed in the cylinders of the subsequent ignition order for the number of times corresponding to the number of intervals, and fuel injection is performed again in the cylinder of the next ignition order. For example, in the case of the engine 1 having an ignition order of the first cylinder - the third cylinder - the fourth cylinder - the second cylinder, the following fuel injection can be performed according to the number of ignition orders of the intervals provided between the ignition orders of the fuel injection.

[0054] <Interval 1 time> First cylinder: Injection - Third cylinder: Fuel cut - Fourth cylinder: Injection - Second cylinder: Fuel cut ··· <Interval 2 times> First cylinder: Injection - Third cylinder: Fuel cut - Fourth cylinder: Fuel cut - Second cylinder: Injection - First cylinder: Fuel cut - Third cylinder: Fuel cut - Fourth cylinder; Injection ··· <Interval 3 times> First cylinder: Injection - Third cylinder: Fuel cut - Fourth cylinder: Fuel cut - Second cylinder: Fuel cut ···

[0055] As described above, according to the second embodiment, in addition to the effects similar to those of the first embodiment described above, by setting the interval of fuel injection (combustion) when performing the reduced cylinder fuel injection control to be longer according to the decrease in the allowable torque fluctuation, the torque fluctuation at the time of fuel cut return can be made smoother.

[0056] (Modification example) The present invention is not limited to the above-described embodiments, and various modifications and changes are possible, and these are also within the technical scope of the present invention. (1) The configurations of the engine and the engine control device are not limited to the above-described embodiments, and can be appropriately changed. For example, the cylinder layout, the number of cylinders, the ignition order, the valve drive method, the presence or absence of a supercharger, the fuel injection location (combustion chamber, intake port), the arrangement of sensors, etc. can be appropriately changed. Also, the vehicle type of the vehicle equipped with the engine is not particularly limited. (2) In each embodiment, the order of the cylinders for fuel injection and the cylinders for continuing fuel cut when performing the cylinder reduction fuel injection control is an example and can be changed as appropriate. Also, the number of cylinders to be reduced (the cylinders for continuing fuel cut) is not limited to a constant value, and the output torque of the engine may be gradually changed by changing it over time. (3) In each embodiment, the output torque control of the engine during the cylinder reduction fuel injection control is performed by the number of cylinders to be reduced and the valve lift of the cylinders during fuel cut continuation. However, the method for controlling the pump loss of the cylinders during fuel cut continuation is not limited to this and can be changed as appropriate. For example, a variable valve timing mechanism capable of controlling the valve timing for each cylinder may be used. Also, a variable compression ratio mechanism capable of controlling for each cylinder or a throttle device having an independent throttle valve for each cylinder may be used.

Explanation of Reference Numerals

[0057] 1 Engine P Piston C Cylinder 10 Crankshaft 11 Crank Angle Sensor 20 Cylinder Block 20R Right Cylinder Block 20L Left Cylinder Block 21 Water Temperature Sensor 30 Cylinder Head 30R Right Cylinder Head 30L Left Cylinder Head 31 Combustion Chamber 32 Spark Plug 33 Intake Port 34 Exhaust Port 35 Intake Valve 36 Exhaust Valve 37 Intake Camshaft 38 Exhaust Camshaft 39 Injector 40 Intake System 41 Intake Duct 42 Chamber 43 Air Cleaner 44 Airflow Meter 45 Throttle Valve 46 Intake manifold 47 Intake pressure sensor 50 Exhaust system 51 Exhaust manifold 52 Exhaust pipe 53 Front catalyst 54 Rear catalyst 55 Silencer 56 Air-fuel ratio sensor 57 Rear O2 sensor 60 EGR device 61 EGR passage 62 EGR cooler 63 EGR valve 100 Engine control unit 101 Accelerator pedal sensor 102 Injection control unit 103 Injection quantity correction unit 110 Atmospheric pressure sensor 120 Acceleration sensor

Claims

1. An engine control device for controlling an engine having a plurality of cylinders, comprising: a fuel injection control unit that controls a fuel injection device for injecting fuel into at least one of a combustion chamber and an intake port of the plurality of cylinders, executes fuel cut control for stopping fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied, and when a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is restarted in some of the cylinders where fuel cut has been executed and fuel cut is continued in the other cylinders, causes fuel injection to be performed in all cylinders; an increment correction unit that corrects the fuel injection amount at the first fuel injection of the cylinders in which fuel injection is restarted after the execution of the fuel cut to increase the amount compared to the fuel injection at the second and subsequent fuel injections according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut; wherein the fuel injection control unit sets the number of cylinders in which fuel injection is performed during the period of the reduced-cylinder fuel injection state until fuel injection is performed in all cylinders after the predetermined fuel cut return condition is satisfied to increase as the allowable torque fluctuation set according to the running state of the vehicle increases. An engine control device characterized by the above.

2. An engine control device for controlling an engine having a plurality of cylinders, comprising: a fuel injection control unit that controls a fuel injection device for injecting fuel into at least one of a combustion chamber and an intake port of the plurality of cylinders, executes fuel cut control for stopping fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied, and when a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is restarted in some of the cylinders in the ignition order of the cylinders where fuel cut has been executed and fuel cut is continued in the other cylinders in the ignition order, causes fuel injection to be performed in all cylinders; an increment correction unit that corrects the fuel injection amount at the first fuel injection of the cylinders in which fuel injection is restarted after the execution of the fuel cut to increase the amount compared to the fuel injection at the second and subsequent fuel injections according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut; After the predetermined fuel cut return condition is satisfied, the fuel injection control unit continues the fuel cut for the number of cylinders performing fuel injection during the period in the reduced-cylinder fuel injection state until combustion injection is performed in all cylinders, and sets it to increase in accordance with an increase in the allowable torque fluctuation amount set according to the running state of the vehicle. An engine control device characterized by the above.

3. An engine control device for controlling an engine having a plurality of cylinders, controlling a fuel injection device that injects fuel into at least one of the combustion chambers and intake ports of the plurality of cylinders, and performing fuel cut control to stop fuel injection in all or some of the cylinders when a predetermined fuel cut condition is satisfied. When a predetermined fuel cut return condition is satisfied, after passing through a reduced-cylinder fuel injection state in which fuel injection is resumed in some of the cylinders in the ignition order of the cylinders where fuel cut was performed and fuel cut is continued in the other cylinders, fuel injection is performed in all cylinders. A fuel injection control unit; An increment correction unit that corrects the fuel injection amount at the first fuel injection of the cylinders where fuel injection is resumed after the execution of the fuel cut to increase it with respect to the fuel injection at the second and subsequent times according to the amount of reverse flow air from the exhaust passage to the combustion chamber during the execution of the fuel cut. The fuel injection control unit, sets the ratio of the number of cylinders continuing the fuel cut of the number of cylinders performing fuel injection in the reduced-cylinder fuel injection state to increase in accordance with an increase in the allowable torque fluctuation amount set according to the running state of the vehicle. sets the interval during which the fuel injection is performed in the reduced-cylinder fuel injection state to become longer in accordance with a decrease in the allowable torque fluctuation amount. An engine control device characterized by the above.

4. The fuel injection control unit sets the allowable torque fluctuation amount to increase in accordance with an increase in the deceleration of the vehicle during the execution of the fuel cut. The engine control device according to any one of claims 1 to 3, characterized by the above.

5. The engine has an intake air amount control unit that controls the intake air amount of the plurality of cylinders for each cylinder. The engine control device includes a torque control unit that adjusts the output torque of the engine in the reduced-cylinder fuel injection state by adjusting the intake air amount of the cylinders continuing the fuel cut. The engine control device according to any one of claims 1 to 4, characterized by the above.

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